Fluid dispensers are known in the art for dispensing various viscous liquid and foam compositions. The viscous liquid and foam compositions are typically soaps, shampoos, creams, or lotions and are often found in public restrooms, restrooms in office buildings, and the like. One problem facing these fluid dispensers is at the end of a dispensing cycle a small portion of the fluid being dispense from the dispenser may remain at the exit port of the dispensing nozzle. This small portion of the fluid being dispensed can result in a condition called “stringing”, in which the small portion of the fluid remains attached to the fluid dispensed to the user. For example, when the fluid is dispensed into the user's hand, the small portion of fluid remains attached to both the fluid dispensed in the user's hand and the exit port of the nozzle. As the user withdraws their hand away from the exit port, the small portion of the fluid remains attached to both the user's hand and the exit port of the nozzle, creating an elongated string-like formation of the fluid. Stringing is especially a problem with foam compositions. Stringing can confuse a user, causing the user to focus on terminating the string, rather than the job at hand, for example, washing one's hands.
Alternatively, the small portion of the fluid may remain solely at the exit port of the nozzle. As gravity or other forces act on this small portion of the fluid, the small portion of the fluid may drip from the exit port of the nozzle onto a structure located beneath the exit port, such as a floor, a countertop, or sink. Alternatively, the small portion of the fluid may from a “string” of the fluid form the exit port to the structure beneath the exit port of the nozzle. In each of these situations, the viscous liquid dispenser gives the appearance of wasting the fluid and/or being of poor quality. In addition, having the fluid on surface beneath the nozzle of the dispenser and/or hanging from the exit port of the dispenser is often unsightly, creating a perception of an unclean restroom, and/or presenting a slip hazard to users of the restroom, when the fluid falls to the floor of the restroom.
In response to the dripping and stringing problems, pumps have been developed that have a suck back mechanism. This suck back mechanism creates a suction which draws the small portion of undispensed fluid away from the exit port. The prior art suck back mechanisms where built directly into the pump which draws the fluid from a reservoir. These mechanisms used the recovery/recharging cycle of the pump to draw the small portion of the undispensed fluid back towards the pump. One problem with this configuration is that the opposite forces are being applied to the pump at the same time, which may result in the pump with the suck back mechanism built into the pump operating in a manner which is undesirable. That is, the pump is caused to draw fluid from the reservoir at the same time the pump is drawing the portion of the undispensed fluid from the exit port of the dispensing nozzle. These opposite forces may make the pump susceptible to sticking or ineffectively drawing the fluid from the reservoir. As a result, to ensure proper operation of the pump, the prior suck back mechanisms have a complex structure.
There is a need in the art for a fluid dispenser with a suck back mechanism which operates independently from the pump mechanism and which has a relatively simple structure.